1. Field of the Invention
The present invention relates to a paper feeding device for feeding a sheet of paper from a paper feed cassette removably mounted in a body of equipment such as a copying machine or a printer.
2. Description of Related Art
In such a paper feeding device known in the prior art, a plurality of sheets of paper having different sizes, such as A4 size and B4 size, are stored in different paper feed cassettes corresponding to the different sizes, and the sheets of paper are fed one by one from a desired one of the paper feed cassettes into the body of the equipment. In the case where each paper feed cassette has a pair of sheet holding lugs located at the front corner portions of the cassette, it is common practice to locate a paper feed roller at a position where an outside end of the paper feed roller is spaced about 20 mm from a side edge of the sheets of paper. Accordingly, the position of the paper feed roller for feeding the paper having the A4 size is different from that for feeding the paper having the B4 size. In the case where the body of the equipment has a single cassette loading portion, i.e., a single paper feed opening, it is necessary to change the position of the paper feed roller according to the chosen paper size. There are various techniques in the prior art for changing the position of the paper feed roller according to a paper size.
For example, in a paper feeding device disclosed in U.S. Pat. No. 5,106,072, which is a division of Ser. No. 07/404,904 filed on Sep. 8, 1989 corresponding to United Kingdom Unexamined Patent Publication No. GB 2,225,776 A, and Japanese Patent Publication No. 60-7788, the paper feed roller is automatically moved to a proper position corresponding to a paper size and simultaneously set in this proper position when a paper feed cassette corresponding to this paper size is loaded into the body of the equipment Further, when the paper feed cassette corresponding to a specific paper size is unloaded from the body of the equipment, the paper feed roller is returned to its normal position corresponding to another paper size.
Another example of a prior art paper feeding device will now be described with reference to FIGS. 4 and 5. FIG. 4 is a plan view of an essential part of a prior art paper feeding device 42, and FIG. 5 is a side view of FIG. 4. Referring to FIGS. 4 and 5, the paper feeding device 42 is of a type such that a plurality of sheets of paper 32 stored in a paper feed cassette 31 are offset to the left side (as viewed in FIG. 4) of the paper feed cassette 31. A driving shaft 33 is rotatably supported at its opposite ends from the body of a printer. The driving shaft 33 is adapted to be driven to rotate so as to feed the paper 32 in a direction of arrow 400 shown in FIG. 4. A left feed roller 34a is fixedly mounted on the driving shaft 33, and a right feed roller 34b is axially slidably mounted on the driving shaft 33. The right feed roller 34b is provided with a known one-way clutch 35 so that the rotation of the driving shaft 33 in the paper feeding direction is transmitted to the right feed roller 34b, thereby obtaining integral rotation of the driving shaft 33 and the right feed roller 34b, while the rotation of the driving shaft 33 in the reverse direction is not transmitted to the right feed roller 34b, thereby obtaining idling of the driving shaft 33. That is, the right feed roller 34b is rotatable together with the driving shaft 33 through the clutch 35 in the paper feeding direction, and is axially slidable on the driving shaft 33 in the opposite direction. A compression spring 36 is interposed between the left feed roller 34a and the right feed roller 34b , so that the right feed roller 34b is normally biased to the right (as viewed in FIG. 4) by the compression spring 36. In FIG. 4, the paper 32 of A4 size is denoted by a one-dot chain line, and a portion of the paper 32 of B4 size exceeding the A4 size paper 32 is denoted by a two-dot chain line.
A roller moving lever 37 is pivotally supported on a shaft 38 mounted on the body of the printer. A tension spring 39 is provided between the roller moving lever 37 and the body of the printer to normally bias the roller moving lever 37 to its normal position shown by a dashed line in FIG. 4. The right feed roller 34b is normally biased to its normal position shown by a dashed line in FIG. 4, by the compression spring 36 so as to deflect the roller moving lever 37. Thus, the roller moving lever 37 and the right feed roller 34b are normally held in the respective normal positions by the tension spring 39 and the compression spring 36, respectively.
Further, in the case where the paper feed cassette 31 is an A4 paper cassette for storing the sheets of paper 32 having the A4 size, the A4 paper cassette is provided with a roller moving chip 40 for moving the roller moving lever 37 from the normal position to a specific position shown by a solid line in FIG. 4. That is, when the A4 paper cassette is loaded into the body of the printer, the roller moving chip 40 is brought into engagement with a projection 41 of the roller moving lever 37 to urge the projection 41 to the specific position. In the case where the paper feed cassette 31 is a B4 paper cassette for storing the sheets of paper 32 having the B4 size, the B4 paper cassette is not provided with the roller moving chip 40.
The operation of the paper feeding device 42 mentioned above will now be described. When the B4 paper cassette is loaded into the body of the printer, the roller moving lever 37 is maintained in its normal position shown by the dashed line in FIG. 4 because the roller moving chip 40 is not included in the B-4 paper cassette. Accordingly, the right feed roller 34b is also held in its normal position shown by the dashed line in FIG. 4 by the roller moving lever 37.
In contrast, when the A4 paper cassette is loaded into the body of the printer, the roller moving lever 37 is urged by the roller moving chip 40 of the A4 paper cassette to move from the normal position shown by (he dashed line in FIG. 4 to the specific position shown by the solid line in FIG. 4. Accordingly, the right feed roller 34b is urged by the roller moving lever 37 to move from the normal position shown by the dashed line in FIG. 4 to the specific position shown by the solid line in FIG. 4.
When the A4 paper cassette is unloaded from the body of the printer, the roller moving lever 37 is returned to its normal position by the tension spring 39. Accordingly, the right feed roller 34b is also returned to its normal position by the compression spring 36.
However, in such a paper feeding device, paper having the specific size (e.g., A4 size in the above case) is mostly used, but the paper feed roller is reciprocated between the normal position and the specific position whenever the paper feed cassette corresponding to the specific size is loaded into and unloaded from the body of the equipment in supplying fresh sheets of paper into the paper feed cassette. Such undue reciprocation of the paper feed roller causes wearing at a sliding portion between the paper feed roller and the driving shaft or a pivotal portion between the roller moving lever and the shaft. Accordingly, there is the possibility of malfunction such that the paper feed roller cannot be returned to its normal position because of the worn sliding portion.